A conventional anti-lock brake system ("ABS") monitors the wheels of a vehicle and institutes corrective action when the wheels begin to slip or lock up during braking. When the ABS recognizes that one or more of the wheels are slipping during braking, the system reduces the brake fluid pressure applied to the wheel brake of the slipping wheel. Once the wheel begins turning again, the fluid pressure applied to the wheel brake is gradually reapplied until the wheels begin slipping again. Fluid pressure applied to a given wheel brake can be reduced by providing a fluid pressure relief path to an accumulator. Fluid can then be pumped from the accumulator back into the main ABS braking circuit.
It is important in any braking system circuit to assure that air or other gases are not present in the circuit, as the compressible nature of air inhibits proper braking performance. Accordingly, in conventional braking systems a vacuum is drawn on the braking system circuit to remove all gases before brake fluid is introduced into the braking circuit. In some manufacturing environments it is desirable to prefill portions of the braking circuit with brake fluid prior to connecting such pre-filled portions with remaining portions of the overall braking system circuit. When the final braking circuit is constructed having a pre-filled portion and a non-prefilled portion, it is necessary to draw a vacuum on the non-prefilled portion in order to removes gas from the entire braking system circuit. It is also necessary to include one or more valves which prevent the inflow of brake fluid from the prefilled portion when the vacuum is drawn on the non-prefilled portion. Traditional check valves or coffin valves have been used for such purposes in the past. However, such traditional valves present certain problems including remaining in the braking system circuit continuously and having at least some affect in the braking system circuit even after the valve is no longer needed.